The present invention relates to an improved sub-surface, or in-ground/in-water, heat exchange means incorporating a sub-surface heating mode refrigerant flow regulating device and a cooling mode refrigerant flow regulating device by-pass means, so as to enable additional refrigerant flow around the regulating device in the cooling mode, for use in association with any direct expansion heating/cooling system, or partial geothermal heating/cooling system, utilizing sub-surface heat exchange elements as a primary or supplemental source of heat transfer.
Ground source/water source heat exchange systems typically utilize fluid-filled closed loops of tubing buried in the ground, or submerged in a body of water, so as to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged tubing. Water-source heating/cooling systems typically circulate, via a water pump, water, or water with anti-freeze, in plastic underground geothermal tubing so as to transfer heat to or from the ground, with a second heat exchange step utilizing a refrigerant to transfer heat to or from the water, and with a third heat exchange step utilizing an electric fan to transfer heat to or from the refrigerant to heat or cool interior air space.
Direct expansion ground source heat exchange systems, where the refrigerant transport lines are placed directly in the sub-surface ground and/or water, typically circulate a refrigerant fluid, such as R-22, in sub-surface refrigerant lines, typically comprised of copper tubing, to transfer heat to or from the sub-surface elements, and only require a second heat exchange step to transfer heat to or from the interior air space by means of an electric fan. Consequently, direct expansion systems are generally more efficient than water-source systems because of less heat exchange steps and because no water pump energy expenditure is required. Further, since copper is a better heat conductor than most plastics, and since the refrigerant fluid circulating within the copper tubing of a direct expansion system generally has a greater temperature differential with the surrounding ground than the water circulating within the plastic tubing of a water-source system, generally, less excavation and drilling is required, and installation costs are lower, with a direct expansion system than with a water-source system.
While most in-ground/in-water heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Several such design improvements are taught in U.S. Pat. No. 5,623,986 to Wiggs, and in U.S. Pat. No. 5,816,314 to Wiggs, et al., the disclosures of which are incorporated herein by reference. These predecessor designs basically teach the utilization of a spiraled fluid supply line subjected to naturally surrounding geothermal temperatures, with a fully insulated fluid return line. However, since only the fluid return line is insulated, and since both the supply and return lines are all the same size, without a dedicated smaller sized refrigerant liquid/fluid transport line and a dedicated larger sized refrigerant vapor/fluid transport line so as to facilitate appropriate refrigerant supply and return capacity in a deep well (greater than 100 feet deep) direct expansion application, these predecessor designs are intended for a near-surface (within about 5 to 100 feet of the surface) direct expansion system application, when operating in a reverse cycle mode.
Other predecessor vertically oriented geothermal heat exchange designs are disclosed by U.S. Pat. No. 5,461,876 to Dressler, and by U.S. Pat. No. 4,741,388 to Kuriowa. Dressler""s ""876 patent teaches the utilization of several designs of an in-ground fluid supply and return line, with both the fluid and supply lines shown as being the same size, and not distinguished in the claims, but neglects to insulate either the fluid return line or the fluid supply line, thereby subjecting the heat gained or lost by the circulating fluid to a xe2x80x9cshort-circuitingxe2x80x9d effect as the supply and return lines come into close proximity with one another at various heat transfer points. Dressler also discloses the alternative use of a pair of concentric tubes, with one tube being within the core of the other, with the inner tube surrounded by insulation or a vacuum. While this multiple concentric tube design reduces the xe2x80x9cshort-circuitingxe2x80x9d effect, it is practically difficult to build and maintain and could be functionally cost-prohibitive, and it does not have a dedicated liquid line and a dedicated vapor line. Kuriowa""s preceding ""388 patent is similar to Dressler""s subsequent spiral around a central line claim, but better, because Kuriowa insulates a portion of the return line, via surrounding it with insulation, thereby reducing the xe2x80x9cshort-circuitingxe2x80x9d effect. However, Kuriowa does not have a dedicated liquid line and a dedicated vapor line. The lowermost fluid reservoir claimed by Kuriowa in all of his designs can work in a water-source geothermal system, but can be functionally impractical in a deep well direct expansion system, potentially resulting in system operational refrigerant charge imbalances, compressor oil collection/retention problems, accumulations of refrigerant vapor pockets due to the extra-large interior volume, and the like. Kuriowa also shows a concentric tube design preceding Dressler""s, but it is subject to the same problems as Dressler""s. Further, both Dressler""s and Kuriowa""s designs are impractical in a reverse-cycle, deep well, direct expansion system operation since neither of their primary designs provide for, or claim, an insulated smaller interior volume sized liquid line and an un-insulated larger interior volume sized vapor line, which are necessary to facilitate the system""s most efficient operational refrigerant charge and the system""s compressor""s efficient refrigerant supply and return capacities.
Generally, a design which insulates the supply line from the return line and still permits both lines to retain natural geothermal heat exchange exposure, such as a thermally exposed, centrally insulated, geothermal heat exchange unit, as taught by Wiggs in U.S. patent application Ser. No. 10/127,517, which is incorporated herein by reference, would be preferable over non-insulated lines and over designs which insulate a portion of one sub-surface line. However, while Wiggs"" ""517 Application is an improvement over prior art, in a sub-surface soil application, it could still be subject to some minor short-circuiting effects and to some potentially adverse vapor formation in the liquid line at undesirable locations or times.
In direct expansion applications, supply and return refrigerant lines may be defined based upon whether they supply warmed refrigerant to the system""s compressor and return hot refrigerant to the ground to be cooled, or based upon the designated direction of the hot vapor refrigerant leaving the system""s compressor unit, which is the more common designation in the trade. For purposes of this present invention, the more common definition will be utilized. Hence, supply and return refrigerant lines are herein defined based upon whether, in the heating mode, warmed refrigerant vapor is being returned to the system""s compressor, after acquiring heat from the sub-surface elements, in which event the larger interior diameter, sub-surface, vapor/fluid line is the return line and evaporator, and the smaller interior diameter, sub-surface, liquid/fluid line, operatively connected from the interior air handler to the sub-surface vapor line, is the supply line; or whether, in the cooling mode, hot refrigerant vapor is being supplied to the larger interior diameter, sub-surface, vapor fluid line from the system""s compressor, in which event the larger interior diameter, sub-surface, vapor/fluid line is the supply line and condenser, and the smaller interior diameter, sub-surface, liquid/fluid line is the return line, via returning cooled liquid refrigerant to the interior air handler, as is well understood by those skilled in the trade. In the heating mode the ground is the evaporator, and in the cooling mode, the ground is the condenser.
None of the above-said prior art addresses an improved means of designing a direct expansion system for a reverse-cycle heating/cooling system operation via insulating only one smaller interior diameter, sub-surface, line, designed primarily for liquid/fluid refrigerant transport, which smaller line may be utilized as a supply line in the heating mode and as a return line in the cooling mode, and of not insulating at least one, or two or more combined, larger interior diameter, sub-surface, lines, designed primarily for vapor/fluid transport, which can provide expanded surface area thermal heat transfer as return lines in the heating mode and as supply lines in the cooling mode. While at least two, larger combined interior diameter, vapor/fluid refrigerant transport lines, operatively connected to one, smaller interior diameter, liquid/fluid refrigerant transport line would generally be preferable because of the resulting expanded, and spaced apart, heat transfer surface contact area, instances may arise where only one, larger interior diameter, vapor/fluid refrigerant line, operatively connected to one, smaller interior diameter, liquid/fluid refrigerant line could also be preferable, or where a larger interior diameter vapor/fluid refrigerant line is spiraled around a centrally located, insulated, smaller diameter liquid/fluid refrigerant line could be preferable.
Where a close to zero-tolerance short-circuiting effect is desirable, and where the time and expense of constructing other designs, such as a concentric tube within a tube, or a spiraled single fluid return line and single fluid supply line of the same sized interior diameters, could be financially, or functionally and/or efficiently, prohibitive in a deep well direct expansion application, and where the thermal exposure area of a single geothermal heat transfer line, or tube, could be too centralized and too heat transfer restrictive, a system design improvement would be preferable which incorporated a cost-effective installation method, capable of operating in a reverse-cycle mode in a sub-surface direct expansion application, with close to zero-tolerance short-circuiting effect, with expanded sub-surface heat transfer surface area capacities, and with a liquid refrigerant trap means at the bottom of the sub-surface heat exchange lines to assist in preventing refrigerant vapor migration, from the refrigerant vapor line into the refrigerant liquid line, as is taught in Wiggs"" pending U.S. patent application Ser. No. 10/251,190, which is incorporated herein by reference. However, none of the above-said prior art addresses the most efficient means of regulating the refrigerant fluid flow through the sub-surface refrigerant transport lines when a direct expansion system is operating in the heating mode, and of permitting optimum refrigerant flow rate around the regulating device when the reverse-cycle system is operating in the cooling mode.
Virtually all high-efficiency heat pump systems, including direct expansion heat pumps, utilize thermal expansion valves to regulate refrigerant flow through the evaporator, which is the exterior heat exchanger in the heating mode, and which is the interior air handler in the cooling mode. In the heating mode, for example, the thermal expansion valve is typically a self-adjusting thermal expansion valve, which valve will generally and ideally be situated in the refrigerant transport line at a point as close as possible to where the refrigerant fluid enters the evaporator, and which valve is operatively connected to a floating bulb. The floating bulb senses superheat levels and sends signals to the valve to adjust the refrigerant flow rate so as to obtain efficient system operation, depending on changing heating load and superheat conditions. The operation of self-adjusting thermal expansion valves is well understood by those skilled in the art.
While use of self-adjusting thermal expansion valves is appropriate in the heating mode for air-source and water-source heat pump systems, where the copper heat exchange tubing is all in relatively close proximity and where the valves are readily accessible for servicing, the common use of such self-adjusting thermal expansion valves in direct expansion heat pump systems can be relatively inefficient because the design refrigerant flow tubing length in the evaporator is often 100 feet, or more. Hence, in a typical direct expansion system, operating in the heating mode, any self-adjustment by the thermal expansion valve takes an inordinate amount of time to take effect and to be sensed by the valve. The valve, during the interim, continues to modulate and fluctuate refrigerant flow rates as it xe2x80x9chuntsxe2x80x9d for an optimum setting. This xe2x80x9chuntingxe2x80x9d results in periodic inefficient system operation and in periodic undesirable decreases in supply air temperatures.
The typical utilization of self-adjusting thermal expansion valves in the heating mode of direct expansion heat pump systems presents problems other than the xe2x80x9chuntingxe2x80x9d concerns. Namely, since such valves are bulky, and may periodically be in need of servicing or replacement, they must be installed in an accessible location, which has historically either been inside the compressor unit box, far from the actual evaporator, or near the ground surface, as close as possible to the point where the refrigerant enters the sub-surface evaporator, but still some distance away from the actual sub-surface evaporator. This is a problem because to operate at maximum efficiencies, the expansion device should generally be as close as possible to the actual evaporator.
Thus, the historical perception by some, that a self-adjusting thermal expansion valve should be utilized in the heating mode of a direct expansion system because it provides the highest operational efficiencies, is subject to serious question because of the necessary distance it must be located from the evaporator and because of inherent xe2x80x9chuntingxe2x80x9d problems. In fact, the longer and/or the deeper the sub-surface evaporator heat exchange lines are in a sub-surface direct expansion system, the greater the xe2x80x9chuntingxe2x80x9d problem becomes with a self-adjusting thermal expansion valve.
However, the use of a self-adjusting thermal expansion valve is generally always appropriate in the cooling mode of a high-efficiency heat pump system, regardless of the type of heat pump utilized, including direct expansion heat pumps, since the valve and the floating bulb, which are readily accessible for servicing, can generally always efficiently function together because of the relatively close proximity of the heat exchange tubing within the interior air handler.
One alternative method of regulating refrigerant flow in the heating mode of a direct expansion heat pump is to install a manually adjusting thermal expansion valve in lieu of a self-adjusting thermal expansion valve. Such a valve will eliminate hunting problems since it will not automatically adjust its own setting. However, such a manually adjusting valve generally must still be placed in an accessible location, which could be hundreds of feet above the actual evaporator in a DWDX application. Further, experience has shown that such a manually adjusting valve, when utilized in a near-surface direct expansion application (within 100 feet of the surface), typically requires at least two manual adjustments per year in order for the system to provide adequate and efficient heat. One such adjustment is required in the fall, at the beginning of the heating season, when the ground surrounding the sub-surface heat exchange tubing is relatively warm, as a result of summer conditions and the system""s preceding cooling mode operation, which has been rejecting heat into the ground area surrounding the sub-surface heat exchange tubing. Generally, at least one other adjustment is required during the winter, as the ground surrounding the sub-surface heat exchange tubing has cooled down to winter-time operational temperatures as a result of heat being extracted by the system in its heating mode of operation. A reasonable manual expansion valve setting for a direct expansion system, when the sub-surface ground is warm, is not the same reasonable setting for when the ground is cool. The construction, the operation, and the reasonable settings of a manual adjusting thermal expansion valve is well understood by those skilled in the art.
Thus, the use of a manually adjusting thermal expansion valve in a direct expansion system, particularly in a DWDX system, while eliminating the hunting problem of a self-adjusting thermal expansion valve, has its problems. A manually adjusting valve is comparatively bulky, must be installed in an above ground and/or accessible location, and, as explained, typically must be adjusted and serviced at least twice per year.
Another alternative method of regulating refrigerant flow in the heating mode is to install a refrigerant fluid distributor with a fixed restrictive hole, or orifice, inside, and typically at the center of, a floating, bullet-shaped, finned, piston, which device is commonly referred to by several designations, such as a piston metering device, a single piston metering device, a floating piston assembly, and a pin restrictor. In the heating mode, the piston, within a casing/housing, moves toward a restrictive seal, which only permits refrigerant fluid flow through the piston hole, or orifice, in the center, thereby regulating the amount of refrigerant entering the evaporator. In the cooling mode, as the refrigerant flow changes direction, the piston moves back, or floats back, toward a less restrictive seal which permits refrigerant fluid flow through the hole, or orifice, as well as additionally through the gaps between the exterior fins on the piston. The specific construction and operation of piston metering devices, including the casings/housings within which they are enclosed, are well understood by those skilled in the art. Since a piston metering device has a fixed orifice, the refrigerant fluid flow rate cannot be adjusted, other than by pressure, so as to accommodate changing exterior load requirements, and has, therefore, generally been considered less efficient and has generally not been used in high-efficiency systems such as direct expansion heat pumps. Instead, many direct expansion heat pump systems utilize self-adjusting thermal expansion valves because of their well-known advantages and improved performance in other heat pump designs, which advantages have previously been commonly, although incorrectly, believed by some to equally apply in a direct expansion application.
In fact, a piston metering device can be more efficient in the heating mode of a direct expansion application than expansion valves, particularly in a DWDX application, because the ground at a depth of more than 100 feet is seasonally less affected by changing, and widely varying, above-ground, near surface, atmospheric temperatures, and hunting, or seasonal valve setting adjustments, for an optimum setting may not be necessary. A piston metering device will eliminate hunting concerns, and, since it is not bulky, can be installed in either an above-ground accessible location, or directly at the commencement of the evaporator segment of a sub-surface direct expansion system where efficiencies are generally best.
However, a reason exists for not using a conventional piston metering device alone in a reverse cycle direct expansion heating/cooling system. Testing has also shown that a properly sized single piston metering devise in a deep well direct expansion (xe2x80x9cDWDXxe2x80x9d) system (deep well is herein defined as where sub-surface heat exchange lines are in excess of 100 feet deep), can impair the optimum refrigerant fluid flow when the system is operating in its reverse cycle cooling mode, as the available refrigerant fluid passageway through the hole in the center of the bullet, together with the available fluid passageway around the outside of the bullet through the fins, can be inadequate to maintain an optimum cooling design refrigerant fluid flow rate. This is because the added pressure, via gravity upon the liquid refrigerant in a DWDX application, can dictate the use of a slightly undersized conventional piston metering device, which device would normally be sized to match the compressor in a conventional heat pump application, but which slightly undersized device in a DWDX application, because of the additional liquid pressure, still achieves the compressor design flow rate in the heating mode, but which undersized device can be a potential impairment to the compressor design flow rate in the cooling mode.
Further, if one elects to install a piston metering device in an above ground and/or an accessible location, the piston size can be easily changed to accommodate changing temperature conditions, or multiple such devices of varying sizes can be installed in series with a pressure and/or temperature means to automatically activate the preferred sized device and to deactivate the rest, by means of a remotely actuated valve such as a solenoid valves, or the like. The installation and operation of remotely actuated valves, such as solenoid valves, and the like, are well understood by those skilled in the art, and, therefore, are not shown herein.
Consequently, a means to provide an efficient refrigerant flow regulating device in a direct expansion, reverse-cycle, heating/cooling system, operating in the heating mode, without xe2x80x9chuntingxe2x80x9d problems, which device does not necessarily require maintenance access, which device is either in close proximity to the actual evaporator or which device can optionally compensate for significant changes in sub-surface temperature environments without the need for manual adjustments, and which device does not inhibit the full refrigerant flow in a reverse cycle cooling mode operation, would be preferable. The present invention provides a solution to these preferable objectives, as hereinafter more fully described.
It is an object of the present invention to further enhance and improve the efficiency of predecessor direct expansion, geothermal, reverse-cycle, heating/cooling system designs. This is accomplished by means of providing a piston metering device apparatus to efficiently regulate refrigerant fluid flow in the sub-surface evaporator segment of a direct expansion heating/cooling system when operating in the heating mode, which device can be optionally designed to accommodate significant sub-surface temperature fluctuations without manual adjustments, and which device does not necessarily require maintenance access, while also providing a non-restrictive refrigerant fluid piston metering device by-pass means, so as not to inhibit reverse-cycle system operational efficiencies when the system is operating in the cooling mode.
The present invention teaches to accomplish the stated preferable objectives by one of several alternative means. The first means consists of at least one smaller, preferably insulated, interior diameter liquid/fluid refrigerant transport line connecting to at least one larger interior diameter vapor/fluid refrigerant transport line at a point near the bottom of a direct expansion system borehole, where at least one single piston metering device, within a piston metering device casing/housing, is respectively installed at each respective point where a smaller interior diameter liquid/fluid line connects to at least one larger interior diameter vapor/fluid line. When the system is operating in the heating mode, this will provide for an even refrigerant fluid distribution, in a relatively stable sub-surface temperature environment, particularly at DWDX depths in excess of 100 feet, and will eliminate the need for an inefficient, xe2x80x9chuntingxe2x80x9d, thermal expansion valve, which valve must be generally placed a significant, and operationally inefficient, distance away from the point of the actual respective evaporator/vapor line connection point so as to provide accessibility for service/repair work.
As a design example, in a vertically oriented, three-ton system capacity, borehole, which is 375 feet deep, an insulated liquid/fluid refrigerant transport tube, such as a xc2xdxe2x80x3 O.D. copper refrigerant tube, is installed about 375 feet deep to a point at or near the bottom of the borehole. The bottom end of the liquid/fluid refrigerant transport tube is preferably bent in a U shape, so that the U shaped lower end of the liquid line extends approximately one foot above the base of the borehole, and is then operatively connected to at least one vapor/fluid refrigerant transport tube, such as a xe2x85x9exe2x80x3 O.D. copper refrigerant tube, of about 374 feet deep for example. The preferable, but not mandatory, U bend in the liquid line acts as both a liquid and a compressor lubricating oil trap, thereby helping to prevent refrigerant migration into the liquid line, and helping to ensure an adequate return of compressor lubricating oil to the compressor. The liquid/fluid refrigerant transport line has a smaller interior diameter than the larger interior diameter vapor/fluid refrigerant transport line. The vapor/fluid refrigerant transport tube, or line, is in direct thermal contact with the sub-surface elements, which elements may consist of one or more of earth, rock, clay, sand, water, anti-freeze, water and anti-freeze, fluid, thermal grout (such as a thermal grout 85 mixture), or the like. The smaller interior diameter liquid/fluid refrigerant transport tube is insulated in most applications so as to avoid a xe2x80x9cshort-circuitingxe2x80x9d effect of the geothermal heat gain/loss since the vapor and the liquid lines are typically in close proximity to one another in a deep well direct expansion, or analogous, heating/cooling application.
Further, as explained, testing has shown that, while single piston metering devices work well in the heating mode of a direct expansion application, as described herein, when installed at the connection point between a smaller interior diameter sub-surface liquid/fluid refrigerant line and a larger interior diameter sub-surface vapor/fluid refrigerant line, a single piston metering device, particularly in a DWDX application, can be too restrictive, and may not provide adequate refrigerant fluid flow rate capacity when a reverse-cycle direct expansion system is operating in the cooling mode. Consequently, the present invention includes means for providing an adequate piston metering device refrigerant fluid by-pass for use in the cooling mode operation.
One such refrigerant fluid by-pass means encompasses an extra smaller interior diameter liquid/fluid refrigerant transport line by-passing the single piston metering device in the cooling mode, installed at a point within about six inches to one foot above the single piston metering device, which extra by-pass line is automatically open in the cooling mode, but which extra by-pass line is automatically closed by a check valve, or the like, when the system is operating in the heating mode. While the extra by-pass line may be opened and closed by a remotely actuated solenoid valve, by a single piston valve (identical to a single piston metering device, but with no central orifice opening), or by a check valve, and the like, as is well understood by those skilled in the trade, a single piston valve or a check valve would generally be preferable for utilization in a direct expansion application because of their simple operation and general lack of need for control wiring and/or maintenance/servicing access.
Another alternative, and presently preferred, means for providing an adequate piston metering device refrigerant fluid by-pass for use in the cooling mode operation consists of utilizing an oversized single piston metering device, so as to permit sufficient design flow rate around the device in the cooling mode, and sealing part of the center orifice, so as to restrict the flow to the desired output in the heating mode. For example, for a 2 ton DWDX system, which would normally utilize a 058 size piston metering device, one could utilize a standard 3 ton single piston metering device, such as a size 067, which would permit an approximate 0.88 gallon per minute flow rate in the cooling mode, which would be entirely sufficient for the operational design of a 2 ton scroll compressor with a 0.59 gallon per minute refrigerant flow rate design, and then seal, with silver solder (15%silver solder) or the like, about 12% or more, depending on depths and refrigerant pressures, of the center orifice opening of the 3 ton device, so as to provide the lesser and optimal desired flow rate when the system is operating in the heating mode.
Alternatively, a single piston metering device, within a piston metering device casing/housing, can be installed in the smaller interior diameter liquid line of a direct expansion system at any accessible above-ground, or very near-surface, location, rather than in the preferable close proximity to the actual evaporator connection. Such an accessible installation will permit servicing and piston size changes if desired, with only a modest potential system operational efficiency reduction, while still eliminating the xe2x80x9chuntingxe2x80x9d problem encountered with self-adjusting thermal expansion valves. Such an above-ground, or very near surface, accessible installation will not require the use of a U shaped liquid trap immediately prior to the installation of the single piston metering device.
Further, when significant seasonal changes in the geothermal temperatures, surrounding the sub-surface heat exchange tubing of a direct expansion heating/cooling system, are anticipated, at least two single piston metering devices of differing sizes, within their respective casing/housing, can be installed in above-ground and/or accessible near-surface locations, in conjunction with solenoid valves and temperature and/or pressure controlled switches designed to activate the desired piston metering device of the appropriate size for the applicable sub-surface temperature conditions, and designed to isolate and de-activate all other piston metering devices of differing sizes. The operation and construction of such temperature and/or pressure remotely activated valves, such as solenoid valves or the like, designed to activate and to isolate selected and respective single piston metering devices, are well understood by those skilled in the art, and, therefore, are not shown herein.
Other customary direct expansion refrigerant system apparatus and materials would be utilized in a direct expansion system application, including a receiver, a thermal expansion valve for the interior air handler, an accumulator, and an air-handler, for example as described in U.S. Pat. No. 5,946,928 to Wiggs, which is incorporated herein by reference, all of which are well-known to those in the art and are therefore not shown herein.
The subject invention may be utilized as an individual unit, or by means of multiple units connected via headers/distributors, connecting sub-surface tubing in series or in parallel by means of common fluid supply and return refrigerant lines, to increase operational efficiencies and/or to reduce installation costs in a number of applications, as is well understood by those skilled in the art. The invention may be utilized to assist in efficiently heating or cooling air by means of a forced air heating/cooling system, or to assist in efficiently heating or cooling water in a hydronic heating/cooling system, as is also well understood by those skilled in the art.